Chapter 2: Units and Measurements


Scientific Method-
is the logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are
supported by data.

Qualitative- descriptive observations of the reaction of the properties of the reactant(color, texture, etc.)

Quantitative- numerical measurement or weighing of anything

System- a specific portion of matter in a given region of space that has been selected for a study during an experiment or observation.

Hypothesis- testable statement that surves as a basis for making predictions and for carrying out further experiments. (if-then statements work)
In an experiment the conditions that remain the same are called constants and what tested that changes is called a variable.

A model in science is more than a physical object; it is often an explanation of how phenomena occur and how data or events are related. Models can be visual, verbal, or mathematical. If a model explains many phenomena, it may become a theory.

A theory is a broad generalization that explains a body of facts or phenomena.


Stages in the scientific method
Observing
-Collecting data

-Experimenting

-Measuring

-Communicating
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Formulating a hypotheses
-Organizing and analyzing data

-Classifying

-Inferring

-Predictions

-Communicating

Testing
-Predicting

-Experimenting

-Communicating

-Collecting data

-Measuring
science_2.jpg
Testing

Theorizing
-Constructing models

-Predicting

-Communicating

Publish Results
-Communicating

A quantity is something that has magnitude, size, or amount. A quantity is not the same as a measurement. For example, the quantity represented by a teaspoon is volume. The teaspoon is a unit of measurement, while volume is a quantity.

Scientist all over the world agreed on a single measurement system called Le Systeme International d’Unites, SI. SI units are defined in terms of standards of measurement.

Weight the measure of the gravitational pull on matter.
Combinations of SI base units form derived units.

Volume is the amount of space occupied by an o bject.

Density is the ratio of mass to volume, or mass divided by volume.

Conversions Factor is the ratio made up of two equal but different units that are used in dimensional analysis.

Dimensional Analysis is a mathematical way to convert different units and get an answer. Often used in stoichiometry to convert grams to moles and then sometimes to another substance

Prefix Chart
Tera

T
10^12
1000000000

Giga

G
10^9
1000000000

Mega

M
10^6
1000000

kilo

k
10^3
1000

Hecto

h
10^2
100

Deka

da
10^1
10



N/A
10^0
1

Deci

d
10^-1
1/10

Centi

c
10^-2
1/100

Milli

m
10^-3
1/1000

Micro

m
10^-6
1/1000000

Nano

n
10^-9
1/1000000000



Pico
p
10^-12
1/1000000000000



Femto
f
10^-15
1/1000000000000000

Atto

a
10^-18
1/1000000000000000000

Accuracy vs Precision Accuracy is producing the correct answer only once without confirmation and precision is producing that same answer multiple times to prove that it is not just coincidence to prove that it is accurate. It is more important to be precise than accurate.

Percent error is found by subtracting true value from experimental value and dividing by the true value. Then multiply by 100. it is used to find how close you were to the accepted answer. For example if the experimental value is 42 and the true is 37 the percent error is 13.5%

Significant Figures (sig figs) are measurements that consist of the digits known plus one that is estimated. The answer can only have as many sig figs as the measurement with the least sig figs in it. If one of the measurements in the equation only has 2 sig figs then the final answer can only have 2 sig figs.
Rounding sig figs- Rounding is all the same except for 5. it will always round to the even number. 16.5 à 16 and 17.5 à 18

Scientific Notation is a form of notation in which the value is very large, and the scientists change it around to make it more managable. The first value in Scientific Notation is greater than 1 but less than 10. An example of Scientific notation is 3.47*10^14 or 3.47E14

Density is the mass to volume ratio. D=m/v

Archimedes' principle is used to calculate the volume of an irregularly shaped object. He discovered that the amount of water displaced is the same as the objects mass.
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